At 09:25 AM 4/14/2005 -0300, you wrote:

>Hi,
>I need some information on how to digitalize the X-rays applied to a body.
>(Replacing the x-ray film, obviously). It is not to make a device, only the
>theory of operation and some diagrams. I have heard there are to methods:
>direct and indirect. Via phosphor material or directly to a phototransistors
>array.There is a lot of info in web but no deep information about the
>electronics implied.

First, I'd recommend you do a search for digital radiography, that will put you
in the right field.
And take a look at this page: http://www.bh.rmit.edu.au/mrs/DigitalRadiography/
it has a whole lot of information on direct x-ray stuff.  Maybe it has an 
explanation.
I'm sure that it has diagrams.

It's been a few years, but the following is what I remember (ie. it may not 
be 100% correct)
about xray scanners from my engineering classes:

In a flat panel direct conversion detector, the x-rays cause electron hole 
pairs to be generated
in a semiconductor as the xrays pass through the semiconductor.  I think 
that is based on some photoconduction phenomenon or something. Anyway, 
standard semiconductor electronics apply
to the holes and the image is generated based on the change of current(?) 
through the semiconductor
as the holes get bigger. I can't remember if they measure current, voltage, 
or resistance change, but
for some reason I think it's the current. Maybe someone else can clarify 
what is being measured.
You can compare these to your standard computer photo scanner except 
replace the fluorescent
lamp with a x-ray tube. And I bet you can find many detailed articles on 
photoscanners.

In a flat panel indirect conversion dectector, the xrays excite phospher 
which emits light, the light
is bent by a mirror and detected by photodiodes which turn the light into 
an electric signal. The
mirror is used to protect the photodiodes from the xrays. It's kind of like 
a television working in reverse -
where light produces the image on the screen and the screen converts the 
image into a signal.
Try searching for scintillator or xray astronomy for better explanations of 
this one.


>Also, -as a bonus- a comparison between Toshiba, General Electric and
>Siemens.

Have you tried calling them and asking them how they work?  Their sales 
engineers
are used to explaining things to medical doctors who usually know very 
little about electronics,
so they can explain things in a simple manner and they should know enough
to answer your questions. And I'm willing to bet that they have some nice 
glossy sales
brochures with diagrams in them.

The only thing I can compare about the companies is that around here, the 
hospitals
all have general electric machines, and the universities have siemens. I've 
never even
seen a toshiba xray machine.

Good luck with your research and if you still can't find anything, then let 
me know and
I'll dig out the text books that have an explanation in them.
_____________________________________________________________
Cris Wilson
Information Resource Consultant
College of Architecture, Arts, and Humanities
Clemson University
cris@clemson.edu
To report problems email: aah_computers@clemson.edu




                                

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